You might consider John MacFarlane's pandoc: http://johnmacfarlane.net/pandoc/
It's Markdown with fixes, pretty ASCII tables, and---best of all---a real parser with a delcarative spec, instead of the ordered-regex nightmare from the original Markdown.

I'm a big fan of John Gruber's Markdown. When it comes to humane markup languages for the web, I don't think anyone's quite nailed it like Mr. Gruber. His philosophy was clear from the outset: Markdown is intended to be as easy-to-read and easy-to-write as is feasible. Readability, however, ...